Gut bacterial diversity of farmed sea cucumbers Apostichopus japonicus with different growth rates.

Farmed sea cucumbers ( Apostichopus japonicus) of the same age displayed significantly different body sizes and weights under the same farming conditions. To examine the gut bacterial diversity of sea cucumbers and whether the growth differences between them were related to intestinal microbiota, the bacterial species from intestinal samples of 30 farmed A. japonicus from the same tank (15 large sea cucumbers vs. 15 small sea cucumbers) were characterized based on 16S rRNA gene analysis by means of high throughout sequencing. The results showed that bacterial phylotypes in both sizes of sea cucumbers were closely related to Proteobacteria, Verrucomicrobia, Bacteroidetes, Actinobacteria, Firmicutes, Cyanobacteria, Planctomycete, and Spirochaetes, of which Proteobacteria were predominant (>50%). There were no significant differences in the relative abundances of each bacterial phylotype between the two groups, except for Actinobacteria ( P < 0.05). In addition, different species uniquely belonging to all three tested samples in the large group and the small group were found. It was interestingly that Vibrio were absent from both groups. It is likely that the differences in the abundances of Actinobacteria and different species in the two groups may be related to their remarkable disparities in body sizes. [ABSTRACT FROM AUTHOR]